Each of the 25 blocks of four letters shown above can be rotated about its center, either 90o clockwise, 90o anti-clockwise or 180o. When all the blocks are in their correct orientations, all the ten rows and columns contain the letters A to J exactly once.

Sixteen of the blocks shown above are not in their correct orientations. Which 16 out of the 25 blocks have been rotated and in which direction(s)?